The invention relates to an acoustic surface wave component, for which the metallic strip structures are coupled mechanically with a piezoelectric material. Such components can be used, for example, as filters, acoustooptical modulators, actors, convolvers or sensors.
The strip structures of known acoustic surface wave component are based on aluminum and are subject to acoustomigration under load, especially when high performances and amplitudes are realized. At the same time, the material of the strip structures is transported partially. This leads to the formation of cavities and strip interruption, on the one hand, and to hill growth and lateral excrescences on the other. The partial delamination of the strip structures can represent further characteristics of damage. These changes bring about an impairment of the function of the component, such as a displacement of the filter frequency when filtering or of the whole filter characteristics with respect to admittance and insertion attenuation, up to the total failure of the component.
Various technical solutions are already known for decreasing acoustomigration. One of the solutions consists of the use of highly textured or monocrystalline aluminum layers for producing the strip structures. However, such a procedure has the disadvantage that it is very expensive to manufacture strip structures.
A different procedure consists of using two-layer aluminum layers, the aluminum being alloyed with small amounts of a different element, especially with copper or titanium, layers with alloys of different composition being combined (U.S. Pat. No. 4,775,814).
Multi-layer systems with up to eleven aluminum layers are also known, in each case an aluminum-free intermediate layer of, for example, titanium or copper, being disposed as a migration inhibitor with a larger elastic component between the individual aluminum layers, which represent the main components of the layer system (U.S. Pat. No. 5,844,374). Technically, it is very expensive to produce strip structures on this basis.
In the case of leaky mode components, it is known that the aluminum strip structures may be provided with a hard covering layer, such as a layer of aluminum oxide, silicide or boride (DE 197 58 195). The layer is either applied or produced by reaction with the aluminum. However, the substrate, as well as the thickness of the coating and of the metallizing must be adapted to the wave type, so that only a slight attenuation of the surface waves is brought about.
An acoustic surface wave arrangement is also known, for which monocrystalline copper layers, grown on a diamond substrate, are used to decrease migration effects (DE 693 07 974 T2). However, the technical effort and the costs for a technological transformation of these monocrystalline layer systems are very high. It is probably hardly possible to realize this technique industrially with the required reproducibility and cost effectiveness. Moreover, it is generally difficult to produce monocrystalline copper, since, according to the present state of knowledge, a very small lattice mismatching is required between layer and substrate and, with that, this technique cannot be employed without a buffer layer for the most frequently used piezoelectric substrate materials, such as LiNbO3, LiTaO3 or quartz.